Line of sight rule?

[Rekka360]

One of my players (an invoker) has a daily utility called the "Walls of Hestavar" which basically lets him raise a 2 square high wall, 10 squares long.

For a particular encounter that I have planned for the party, monsters will be throwing Alchemical Acid or Fire (in vials) at the party. Now: provided that the party invoker raises a Wall of Hestavar, which in its description says that it "blocks line of sight" if these monsters want to just throw the vials of alchemical acid or fire at random over the wall, how would that work?

They can't target the party directly (since they can't see them), but it seems like they should be able to still lob stuff over the wall.

Ideas?

 

[Mummolus]

Total concealment (-5 penalty to attack rolls), at least. Picking a square at random (via a dice roll) plus total concealment, most likely.

 

[Chronosome]

Total concealment (-5 penalty to attack rolls), at least. Picking a square at random (via a dice roll) plus total concealment, most likely.

Good ruling. I'd throw in a Perception (DC +10 "through a wall", at least) check to guess which square the creatures might be in.

 

[mneme]

Line of sight isn't an issue, here, as you don't need line of sight for a burst 1. Neither is total concealment.

But line of effect is; the abilty doesn't say the wall blocks LoE, but as a solid obstacle, it should. I'm fine with ruling that throwing a grenade-like weapon over the wall will let you bypass this, but I'd want to make the thrower roll to hit the square they were aiming for (roll to hit the easy number for the level from p42, plus 7 for cover + total concealment, maybe? On a miss, I'd roll D8 for a direction and d6-d6 for distance). I'd resolve the burst normally for anyone caught in it.

Note that the party can move with stealth, as they have total concealment, so the bad guys might not know which squares they are in or vice versa.